Bougainvillea, with vibrant, paper-like bracts, adds color to gardens. Brown spots on leaves are a common issue, indicating underlying problems like environmental stress or pest infestations. Understanding causes is the first step to diagnosis and restoring plant health.
The Foundation of Bougainvillea Health
Bougainvillea thrives with ample sunlight (at least six hours daily) for colorful bracts and well-draining soil to prevent root issues. Established bougainvillea is drought-tolerant, but consistent watering during establishment is important, allowing soil to dry slightly between waterings.
Common Causes of Brown Spots and Their Solutions
A. Watering Imbalances
Both insufficient and excessive watering cause brown spots. Underwatering results in dry, crispy brown spots, leading to wilting and premature leaf drop; water deeply until drainage. Overwatering causes soft, mushy brown spots, often with yellowing and root rot; ensure excellent drainage and water only when soil has dried.
B. Sunlight Extremes
Bougainvillea needs direct sunlight, but intense sun can scorch leaves, causing bleached or crispy brown spots. In extreme sun, provide afternoon shade or gradually acclimate. Insufficient light weakens the plant, making it vulnerable to discoloration; ensure at least six hours of direct sunlight daily for health.
C. Temperature Stress
Bougainvillea is sensitive to temperature extremes, especially cold. Frost damage turns leaves black or dark brown, potentially leading to defoliation. Protect plants from cold snaps by covering or moving potted plants indoors below 40°F (4°C). Excessive heat, especially with low humidity, stresses the plant, causing wilting and browning. Ideal temperatures range between 60-95°F (15-35°C); during heatwaves, ensure hydration.
D. Nutrient Deficiencies
Nutrient deficiencies can cause leaf discoloration and browning. Lack of phosphorus or potassium manifests as brown or purple edges on older leaves. Iron deficiency results in yellowing between new growth veins. A balanced, slow-release fertilizer during the growing season prevents these issues. Avoid over-fertilization, especially with nitrogen, as this promotes leafy growth at the expense of blooms and causes leaf burn.
E. Pests and Diseases
Pests cause brown spots or discoloration. Spider mites, thriving in hot, dry conditions, feed by sucking cell contents, resulting in stippled or speckled leaves that turn yellow or bronze before browning. Aphids and scale insects are other sap-sucking pests causing discoloration and weakening. Fungal and bacterial leaf spot diseases are common, presenting as distinct dark brown or black spots. These diseases are favored by warm, humid conditions and poor air circulation. Removing infected leaves and improving air flow helps manage spread. Root rot, a fungal disease, also causes wilting, yellowing, and browning.
F. Chemical Burns
Improper chemical application (herbicides, fertilizers) can cause brown, scorched spots. Herbicide drift results in irregular browning patterns. Over-fertilization leads to salt buildup and chemical burn. Follow product instructions carefully: dilute liquid fertilizers and water thoroughly after granular products. Apply chemicals during cooler parts of the day to reduce scorching.
Preventing Future Brown Spots
Preventing brown spots requires consistent care. Key practices include:
- Maintaining a regular watering routine, allowing soil to dry between deep waterings.
- Ensuring at least six hours of direct sunlight daily.
- Protecting plants from sudden temperature drops, especially frost.
- Providing regular, balanced fertilization during the growing season.
- Routinely inspecting for pests or diseases.
- Ensuring good air circulation through proper spacing and occasional pruning.
When to Seek Expert Help
If brown spots persist or plant health declines, seek professional advice. Local garden centers, university extension offices, or plant pathologists offer diagnostic services.